In BA Guide on page no.90, there is a mention of Use Case Diagram in Scope Model and Use Case in Process Model. I would like to know if there is any difference between these two. If they are not same, then can you pls. give me a figure where the Use Case diagram and text are combined.

Use Cases: The purpose of use case is to capture the interaction of a user with the system in the context to achieve a Goal. The use case is the set of scenarios tied together by a common user goal.

I have added a PDF in chapter 5 - "Process Model Clarification Session" as item 15. Please go through it and let me know if any confusion in the understanding of Use Cases.

Use Case Diagram: These are normally referred to describe a set of actions at the high level. While Use Cases includes set of scenarios in textual format, so it helps in understanding a process of an action. Use case diagram only helps in understanding high-level features, that's why it is in scope model.

It is not needed to convert each use case diagram into use cases as it may increase the complexity. When you have understood the features at the high level, next level detailing can be done using use cases.